(CBS) MARIETTA, Georgia - Opening statements launched Tuesday in the trial of De'Marquise Elkins, the Georgia man accused of fatally shooting 13-month-old Antonio Santiago as the child was being pushed in a stroller by his mother.

Tuesday, prosecutors said Elkins shot the child when the mother didn't immediately turn over her purse, while a defense attorney suggested the child's parents had a financial interest in the child's death and could be somehow involved in the slaying.

De'Marquise Elkins is charged with murder and other offenses in the March 21 killing of the toddler.

"The young man took the gun and aimed it at Antonio's head and shot him right between the eyes," Brunswick District Attorney Jackie Johnson told jurors.

If convicted, Elkins will not face the death penalty because he was 17 at the time of the killing. He is too young under Georgia law to be executed.

The child's mother, Sherry West, was shot in her leg and another bullet grazed her ear. Prosecutors have also accused Elkins of shooting Wilfredo Calix Flores outside a local church 10 days before the child was killed.

The killing this spring in the port of city of Brunswick, close to vacation spots like Jekyll Island, drew national attention, and the trial was moved to the Atlanta suburbs because of the extensive publicity the case received locally. In opening statements, Johnson told jurors that both shootings started off as robberies.

"When it didn't happen immediately, as Mr. Elkins thought it should, his reaction was to shoot," Johnson alleged.

Sherry West breaks down in tears as she describes the death of her son, who was shot while she pushed him in a stroller.

Bobby Haven

The prosecutor said Elkins and an accomplice, 15-year-old Dominique Lang, stopped the mother and child as they returned home from the post office. Johnson said that Elkins pointed a small .22-caliber revolver at West and demanded her money. West did not immediately hand over her purse and the child was shot.

Bystanders and rescue workers were unable to revive the child, who was pronounced dead at the scene.

Lang is also charged as an adult with murder but will be tried separately. Authorities said Lang identified Elkins as the shooter and is expected to testify at the ongoing trial.

Defense attorney Jonathan Lockwood suggested that Antonio's parents were somehow involved in his death, though he did not provide a precise motive or further explain that theory. He said that no one in the neighborhood saw or heard anyone fleeing the scene of the shooting.

He also questioned whether police focused their investigation too soon on the wrong suspects. He said that West tried to collect on a life insurance policy shortly after her son's death.

"The police were under a great deal of pressure to see that the matter was resolved as vacation season was not far away," Lockwood said.

Lockwood said the child's parents both had gunshot residue on their hands. A report filed earlier by the Georgia Bureau of Investigation said that gunshot residue can wind up on shooting victims. The child's father, Louis Santiago, said during an initial court hearing that he touched the bullet wound on West's leg before his hands were swabbed.

Prosecutors said information from Elkins' mother and sister led investigators to a pond where they found a .22-caliber revolver. Elkins' mother, Karimah Elkins, is standing trial alongside her son on charges of evidence tampering and lying to police. Elkins' sister was also charged with evidence tampering.

An attorney for Karimah Elkins, J. Wrix McIlvaine, said police had violated her rights and that she was not involved in the killing.

McIlvaine said, "None of these people had anything to do with the shooting of a child."